Conventional polishing systems and polishing methods typically are not entirely satisfactory at planarizing semiconductor wafers. In particular, polishing compositions and polishing pads can have less than desirable polishing rates, and their use in chemically-mechanically polishing semiconductor surfaces can result in poor surface quality. Because the performance of a semiconductor wafer is directly associated with the planarity of its surface, it is crucial to use a polishing composition and method that results in a high polishing efficiency, uniformity, and removal rate, and leaves a high quality polish with minimal surface defects.
The difficulty in creating an effective polishing system for semiconductor wafers stems from the complexity of the semiconductor wafer. Semiconductor wafers are typically composed of a substrate, on which a plurality of transistors has been formed. Integrated circuits are chemically and physically connected into a substrate by patterning regions in the substrate and layers on the substrate. To produce an operable semiconductor wafer and to maximize the yield, performance, and reliability of the wafer, it is desirable to polish select surfaces of the wafer without adversely affecting underlying structures or topography. In fact, various problems in semiconductor fabrication can occur if the process steps are not performed on wafer surfaces that are adequately planarized.
The use of polyelectrolytes in chemical-mechanical polishing compositions is commonly known in the art. In some cases, the polyelectrolytes are used as complexing agents for the surface layer to be removed. In other cases, the polyelectrolyte is added to modify the properties of the polishing composition by acting as a dispersant, a thickener, or a flocculating agent. For example, the modification of ceria-based slurries for CMP operations using anionic polymers is reported by H. Nojo, M. Kodera, and R. Nakata, “Slurry Engineering For Self-stopping, Dishing Free SiO2-CMP,” IEDM, pp. 349-353 (1996), where polyacrylic acid or ammonium polyacrylate is used to obtain self-limiting polishing. U.S. Pat. No. 6,443,811 describes a ceria slurry where the addition of surfactants and/or a non-ionic such as polyacrylamide or polyvinyl alcohol having a molecular weight of less than 10000 is effective to reduce defects. U.S. Pat. No. 5,876,490 discloses a slurry composition comprising abrasive particles and a polyelectrolyte wherein the charge on the polyelectrolyte is different from the charge on the abrasive particles. U.S. Pat. No. 6,540,935 describes a ceria slurry having poly-vinyl sulfonic acid and potassium hydrogen phthalate, each a passivator. U.S. Pat. No. 6,616,514 teaches a slurry having ceria and one of mannitol, sorbitol, mannose, xylitol, sorbose, sucrose, and dextrin, but notes that increased selectivity is accompanied by slower polishing rates. U.S. Pat. No. 6,514,821 teaches a slurry having ceria and a polycarboxylate. U.S. Pat. No. 6,443,811 describes minor polishing increases when for example proline, glycine, or alanine is added to the slurry.
And still, in yet other cases, the polyelectrolyte is used to modify the surface of the abrasive particle. The following patents and patent applications disclose polishing compositions comprising polyelectrolytes that purportedly complex the surface of the substrate. U.S. Pat. No. 6,561,876 describes increasing the rate of polishing of a ceria slurry by the weak adsorption of a surfactant such as ammonium polyacrylate or an organic amine salt to an abrasive grain, that the surfactant can be easily desorbed from the abrasive grain on the occasion of polishing. U.S. Pat. No. 6,099,604 discloses a polishing composition comprising a solvent, abrasive particles, and a polycarboxylic acid chelating agent. The chelating agent purportedly stabilizes portions of the substrate that are dislodged by the chemical-mechanical polishing process. International Publication No. WO 99/64527 discloses a polishing composition comprising water, an abrasive, an oxidizer, optionally a complexing agent and/or a dispersant, and an organic polymer to attenuate removal of an oxide film. International Publication No. WO 01/14496 discloses a polishing composition comprising an organic polymer with a backbone containing at least 16 carbons, and optionally abrasive particles, dispersing agents that prevent agglomeration of the abrasive particles, oxidizing agents, and complexing agents. The organic polymer is designed to adhere to the surface of a polished wafer, thereby eliminating scratching and redeposition of residue. U.S. Pat. No. 6,117,775 discloses a polishing composition comprising less than 1 wt. % abrasive particles, oxidizing agents, organic acids, and surfactants which purportedly suppress etching and oxidation. U.S. Pat. No. 6,303,049 discloses a polishing composition comprising an abrasive, an abrasion enhancer (e.g., phosphorous acid), and a water-soluble anionic chemical (e.g., a acrylate, phosphate, sulfate, or sulfonate-containing compound, polymer, and/or copolymer). The anionic chemical purportedly coats the surface of the metal film during polishing.
Published U.S. Application No. 2003/0124959 describes particles coated with polystyrenesulfonic acid (or any negatively charges copolymer having one or more sulfonic acids, sulfonates, sulfates, phosphonic acids, phosphonates, and/or phosphates with a molecular weight greater than 20,000 Daltons) coated onto particles such that the zeta potential is thereby lowered. Published U.S. Application No. 2003/0124959 discloses a method for copper CMP using polymeric complexing agents having a defined molecular weight range that bind to abrasive particles in aqueous solutions to modify the surface characteristics of the abrasive particles (i.e., to reduce the zeta potential thereof, which, according to paragraph 45 and Example 2, increases the colloidal stability of the abrasive particles in solution). The disclosure at paragraph 6 distinguishes this surface modification function from other functions such as complexing agent for the substrate surface layer ions and property modification of the CMP composition (e.g., where the polymeric complexing agents can be used as a dispersant, a thickener, or a flocculating agent). The publication discloses at paragraph 30 that the polymeric complexing agents have monomers selected from the group consisting of styrene sulfonic acid, vinyl sulfonic acid, vinyl phosphonic acid, and 2-acrylamido-2-methylpropane sulfonic acid (AMPS), optionally with nonionic monomers such as ethylene oxide, propylene oxide, or styrene. The preferable polymeric complexing agent is taught at paragraph 38 to be poly(acrylic acid), poly(acrylic acid-co-AMPS), or a combination thereof. The publication, however, does not disclose or suggest diluent-insoluble or crosslinked polymeric complexing agents that do not associate with abrasive particles. Further, the publication does not disclose or suggest the combination of its complexing agent-coated abrasives with completely complexing agent-uncoated abrasives in CMP compositions or methods.
The following patents and patent applications disclose polishing compositions comprising polyelectrolytes that purportedly act to modify the properties of the polishing compositions. U.S. Pat. No. 4,752,628 discloses a polishing composition consisting of finely divided inorganic abrasive, a biocide, carboxylic acid dispersant polymer, carboxylic acid polymer thickener, corrosion inhibitor, and optionally a lubricant. U.S. Pat. No. 4,867,757 discloses a polishing composition with a pH greater than 8.5 consisting of finely divided inorganic abrasive, carboxylic acid dispersant polymer, and a lubricant. U.S. Pat. No. 5,123,958 discloses a polishing composition comprising an abrasive, a gel-type carrier comprising a polyvinyl alcohol and water mixture, and optionally a polyelectrolyte flocculating agent. U.S. Pat. No. 5,352,277 discloses a polishing composition comprising water, colloidal silica, a water-soluble polymeric compound, and a water-soluble salt at alkaline pH. The polymeric compound purportedly aids in forming a regular laminar flow between the polishing pad and the substrate surface during polishing. U.S. Pat. No. 5,860,848 discloses a polishing composition comprising water, submicron silica particles, a salt, an amine compound, and a polyelectrolyte at pH 8-11. The polyelectrolyte purportedly reduces particle adhesion to the substrate surface. U.S. Pat. No. 6,117,220 discloses a polishing composition comprising water, polystyrenesulfonic acid, an inorganic or organic acid, and an abrasive. The polystyrenesulfonic acid purportedly functions to flocculate the abrasive particles producing a polishing composition with good anti-foaming properties and low incidence of surface pitting during chemical-mechanical polishing. U.S. Pat. No. 6,117,783 discloses a polishing composition comprising a hydroxylamine compound and sufficient polyelectrolyte to repel particles away from each other and the surface of the substrate. U.S. Pat. No. 6,132,637 discloses a polishing composition comprising an aqueous medium, an abrasive, a surfactant, an organic polymer, and a complexing agent with two or more acid groups capable of complexing silica and silicon nitride. The organic polymer purportedly acts to enhance the viscosity of the polishing composition and to inhibit scratching of the substrate being polished with the polishing composition. U.S. Pat. No. 6,171,352 discloses a polishing composition comprising an aqueous medium, abrasive, an abrasion accelerator, and optionally a nitrate salt or anionic surfactant (e.g., polycarboxylic acid) that reduces the viscosity of the polishing composition. Japenese Patent No. JP-1087146 discloses a polishing composition comprising an abrasive and polystyrene sulfonic acid, which purportedly is used as a dispersant and improves polishing performance.
The following patents and patent applications disclose polishing compositions comprising abrasive particles that purportedly electrostatically interact with the polyelectrolyte. U.S. Pat. No. 5,876,490 discloses a polishing composition comprising abrasive particles and a polyelectrolyte (molecular weight of 500 to 10,000) with a charge that differs from that of the abrasive particles. The polyelectrolyte purportedly coats the surface of the abrasive particles leading to improved polishing behavior. European Patent No. EP-1 036 836 A1 discloses a polishing composition comprising an aqueous dispersion of polymer particles of thermoplastic resins and inorganic particles that have opposite zeta potentials and are bonded by electrostatic force. Similarly, European Patent No. EP-1 104 778 A2 discloses a polishing composition comprising composite particles consisting of inorganic particles and polymer particles of opposite zeta potential. European Patent No. EP-1 118 647 A1 discloses a polishing composition comprising an abrasive, an oxidizer, a co-oxidizer, and an anti-coagulation agent. The anti-coagulation agent is purportedly used to stabilize molecular weight is described for the anti-coagulation agent. Japanese Patent No. JP-200164631 discloses a polishing composition comprising abrasives and a polymer or copolymer comprising sulfonic acid groups (molecular weight of about 5,000 to about 20,000). The polymer purportedly adheres to the polishing waste created during chemical mechanical polishing. International Publication No. WO 01/02134 discloses a polishing composition comprising an aqueous medium and abrasive particles that are maintained in a meta-stable phase by the presence of ionic species (e.g., polyelectrolytes and surfactants) that coat the surface of the abrasive particles.
Compositions and methods for planarizing or polishing the surface of a substrate, especially for chemical-mechanical polishing (CMP), are well known in the art. Polishing compositions (also known as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the polishing composition. Typical abrasive materials include silicon oxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No. 5,958,794 discloses a fixed abrasive polishing pad. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.